18 March 2015

The longer a mother breastfeeds, the higher the IQ and salary

by Will Parker

Published in The Lancet Global Health journal, a study that tracked more than 3,000 newborns for 30 years has concluded that the longer a mother breastfeeds, the greater the intelligence and earnings of the offspring.

"The effect of breastfeeding on brain development and child intelligence is well established, but whether these effects persist into adulthood is less clear," explained lead author Dr Bernardo Lessa Horta, from the University of Pelotas in Brazil. "Our study provides the first evidence that prolonged breastfeeding not only increases intelligence until at least the age of 30 years, but also has an impact both at an individual and societal level by improving educational attainment and earning ability."

What is unique about this study is that in the population studied, breastfeeding was not more common among highly educated, high-income women, but was evenly distributed across social classes. Previous studies from developed countries have been criticized for failing to disentangle the effect of breastfeeding from that of socioeconomic advantage, but the new work addresses this issue for the first time.

Horta analyzed data from nearly 6,000 infants born in Brazil in 1982, collecting breastfeeding information in early childhood. Three decades later, the participants were given an IQ test (Wechsler Adult Intelligence Scale, 3rd version) at the average age of 30 years old and information on educational achievement and income was also collected.

Information on IQ and breastfeeding was available for just over half (3,493) participants. The researchers divided these subjects into five groups based on the length of time they were breastfed as infants, controlling for 10 social and biological variables that might contribute to the IQ increase including family income at birth, parental schooling, genomic ancestry, maternal smoking during pregnancy, maternal age, birth-weight, and delivery type.

While the study showed increased adult intelligence, longer schooling, and higher adult earnings at all duration levels of breastfeeding, the longer a child was breastfed for (up to 12 months), the greater the magnitude of the benefits.

The study shows that an infant who had been breastfed for at least a year gained a full four IQ points, had 0.9 years more schooling, and had higher incomes (an additional 341 reals per month (US$103), equivalent to about one third of the average income level) at the age of 30 years, compared to those breastfed for less than one month.

The study suggests that the effects of breastfeeding on cognitive development persist long into adulthood, and Dr Horta thinks that the chemistry of breast milk is responsible for the effect. "The likely mechanism underlying the beneficial effects of breast milk on intelligence is the presence of long-chain saturated fatty acids found in breast milk, which are essential for brain development. Our finding that predominant breastfeeding is positively related to IQ in adulthood also suggests that the amount of milk consumed plays a role," he said.